1. Technical Field
The present invention relates to an oscillation circuit, an oscillator, an electronic apparatus, and a moving object.
2. Related Art
There is a known method of applying a voltage to a variable capacitance element arranged in an oscillation circuit and changing the capacitance of the variable capacitance element in order to vary the frequency of the oscillation circuit. An oscillator that controls a frequency with a voltage is generally called VCXO (Voltage Controlled X'tal Oscillator). There is also a TCXO (Temperature Compensated X'tal Oscillator) that reduces a frequency deviation with respect to temperature using this principle.
In recent years, quartz crystal oscillators have been reduced in size. Integration of an oscillation circuit is ongoing. However, since a variable amount of a usable variable capacitance element is limited when an integrated circuit is used, a necessary frequency variable width and necessary linearity cannot be obtained.
WO 02/19514 discloses an oscillator in which a frequency adjusting voltage and a temperature compensation voltage are added up by an adder circuit and applied to a frequency adjustment circuit.
In WO 02/19514, the frequency adjusting voltage and the temperature compensation voltage are added up and applied to the frequency adjustment circuit. Therefore, compared with when frequency adjustment and temperature compensation are independently performed, a frequency width that can be varied by the frequency adjustment circuit has to be increased. Therefore, for example, when a variable capacitor is used in the frequency adjustment circuit, compared with when the frequency adjustment and the temperature compensation are independently performed, it is likely that a frequency variable width is insufficient if only a region with high linearity of variable capacitance sensitivity is used. It is likely that the accuracy of the frequency adjustment is deteriorated if a region wider than the region with the high linearity of the variable capacitance sensitivity is used.